The present invention relates to an image forming apparatus which forms an electrostatic latent image onto a latent image carrier by writing electrodes of a writing device being in elastic contact with the latent image carrier.
Among conventional known image forming apparatuses, there is a type of using a large number of needle electrodes to form an electrostatic latent image onto a latent image carrier. In an image forming apparatus of this type of using needle electrodes, an electrostatic latent image is formed onto a latent image carrier by discharge from the needle electrodes. The needle electrodes are employed as discharge portion of this image forming apparatus because such a needle electrode can discharge at the lowest possible starting voltage and has an acute tip that is preferable in terms of improving the image resolution. Generally, the needle electrodes are arranged to have a slight space from, i.e. in non-contact with, the latent image carrier and the formation of an electrostatic latent image onto the latent image carrier is conducted by discharge phenomenon.
However, variation of starting voltage for discharge due to fluctuation in the space directly causes the scatter in potential of the electrostatic latent image, leading to major image defects such as linear stains, irregularities, interruption, blur, and/or dusts. Accordingly, to stably keep the space constant, the needle electrodes are required to have high precision and high rigidity and a holding member of positioning and supporting the needle electrodes is also required to have high precision and high rigidity. In addition, the needle electrodes should be precisely positioned on a bus line of the latent image carrier in the circumferential direction of the latent image carrier. If not, the fluctuation in the space should be occurred and thus uniform charge can not be ensured. Further, run-out of the rotational axis of the latent image carrier is sure to cause fluctuation in the space. For this, spacers are provided for controlling the space. However, in case of high-speed printing in which the latent image carrier rotates at a high ratio, it is hard or impossible to keep the space constant due to vibration. As a result, the printing speed should be set at a lower speed.
As a means for solving the aforementioned problems, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, ""104B publication), in which needle electrodes are kept in contact with a latent image carrier coated by an organic glass and lubricant oil is applied to the latent image carrier to prevent wearing or damage of the latent image carrier due to the contact of the needle electrodes.
However, the invention of ""104B publication has another problem of wearing of the needle electrodes. The wearing of the needle electrodes causes variation in starting voltage for discharge, leading to change in size of the electrostatic latent image and change in charged potential. Since application of oil to the latent image carrier is necessity for reducing the wearing, developing powder such as toner can not directly deposited so that the latent image carrier can only functions as an intermediate image transferring medium.
As mentioned above, the type of using a large number of needle electrodes has a problem that scatter in potential of an electrostatic latent image is easily caused so that the latent image resolution is varied with time, thus deteriorating the quality of obtained images. Since a holding member and/or a positioning member having high precision are required for holding and positioning the needle electrodes and the latent image carrier and the space therebetween, there is also a problem that the apparatus should be complex and large. There are still problems that the electrodes and the latent image carrier should be damaged for a short period of time due to high contact pressure of needle-type electrodes, that high-speed printing is hardly achieved, and that the apparatus should be large because of the use of the latent image carrier as an intermediate image transferring medium.
The present invention is directed to solve the aforementioned problems of the prior art and it is an object of the present invention to provide an image forming apparatus which can forms a high-quality image with high resolution while stabilizing potential and size of an electrostatic latent image and in which the wearing of electrodes and a latent image carrier can be reduced, thereby improving the durability thereof.
To achieve the aforementioned object, an image forming apparatus comprises a latent image carrier and a substrate on which a plurality of writing electrodes are formed along the axial direction of said latent image carrier, and is characterized in that said latent image carrier and said substrate are arranged in elastic contact with each other so as to form an electrostatic latent image on the latent image carrier.
According to the present invention, since the substrate having the electrodes formed thereon is in elastic contact with the latent image carrier, a greater contact nip can be obtained therebetween even with light load and the contact therebetween can be uniform along the axial direction of the lateral image carrier so that the electrode portion well follows the latent image carrier, thereby achieving the stabilized contact therebetween. This design can exhibit the following effects. That is, charge injection for a long period can be achieved so as to produce saturated charge, thereby stably forming high quality electrostatic latent images. This design allows use of low voltage as the voltage to be impressed to the electrodes, thereby reducing generation of ozone. In addition, the pressing force for keeping the writing electrodes in contact with the latent image carrier is small, thus reducing the wearing rate of the electrodes and the latent image carrier, leading to formation of images and improvement in their durability. In addition, this design prevents breakage of insulation due to damages. This design also allows the electrodes to be arranged to have greater distance therebetween, thus reducing the possibility of crosstalk between the electrodes.
Since the writing electrodes can be securely arranged in contact with or in proximity to the latent image carrier with a small pressing force by the flexible substrate, there is little or no gap (space) between the writing electrodes and the latent image carrier. The little or no gap reduces the possibility of undesirable air ionization, thereby further reducing the generation of ozone and enabling the formation of an electrostatic latent image with low potential. In addition, the latent image carrier can be prevented from being damaged by the writing electrodes, thus improving the durability of the latent image carrier.
Further, since the writing device employs only the writing electrodes without using a laser beam generating device or a LED light generating device which is large in size as conventionally used, the apparatus size can be reduced and the number of parts can also be reduced, thereby obtaining an image forming apparatus which is simple and low-price.